As shown in FIG. 1, a microwave transmission apparatus 100 includes a service transmitting device 102 and a service transmitting device 104 which both have a same function. The service transmitting devices 102 and 104 respectively play a primary role and a secondary role. The service transmitting device 102 includes a convergence module 12, an intermediate frequency module 14, a radio frequency module 16, and an ACM engine 18. The service transmitting device 104 includes a convergence module 13, an intermediate frequency module 15, a radio frequency module 17, and an ACM engine 19. The convergence module 12 converges received services to generate multiplexed data and transmitting, at a service clock rate, the multiplexed data to the intermediate frequency module 14 and the intermediate frequency module 15 respectively. The intermediate frequency module 14 and the intermediate frequency module 15 respectively process the multiplexed data, and then perform transmission respectively through the radio frequency module 16 and through the radio frequency module 17, so as to support a 1+1 protection switching function.
In a microwave transmission apparatus 100 in which the ACM is applied, as a transmission capacity changes at any time along with changes of ambient factors such as the weather, to ensure the transmission quality and maintain a high bandwidth utilization ratio, the convergence module 12 is required to correspondingly change a service clock rate for transferring the multiplexed data. Accordingly, the ACM engine 18 is required to change parameters, such as a service modulation mode and an encoding rate, and initiate ACM switching.
During the ACM switching, the service clock rate at which the convergence module 12 sends the multiplexed data changes in different modulation modes, and correspondingly, a rate and a phase of a symbol clock generated by the intermediate frequency modules 14 and 15 in tracking the service clock rate also change, so a system clock generated by a receiver in tracking the symbol clock is unstable, so that the error rate of the service during the transmission is increased.